Microwaves thermal conditioning of preforms

Free blowing of PET preform has been performed successfully and quickly in a rotating system which has been designed for dielectric loss heating. Investigations of the thermomechanical behaviour of PET and biaxial-stretch blow moulding have shown that an inverted temperature profile is needed prior to its stretching. A temperature profile modelling was carried out using the permittivity at different temperatures of the amorphous PET. It was necessary to solve the Maxwellʹs and heat equations to determine the best profile and power tuning. Transient external surface wall predicted temperature was found to agree well with IR result. This work needs further investigation for a complete heating of the preform and better energy efficiency. Industrial application involves the integration of the moulding step and the design of the overall process. So far it has been found that the microwave assisted process is at least five times faster than IR heating.